Hi Corion,
Thank you for your suggestion.
However, I might have left out some criteria though.
1. A,B,C,D.. are headers that I would need to have with their preceding values equated to. eg. A=undef,B=123-456 hh:mm, C=undef,D=789...
2. This would mean that the RHS of the headers would change over time keeping the LHS headers constant.
How would you suggest that I overcome this, please?
Thank you.
Kind Regards,
Cornelius

Oh, of course you left out critical criteria! Answering these questions would not be near as much fun if we actually had accurate problem statements to begin with. I'm sure Corion appreciates the opportunity to waste... er, devote his or her time to providing a useful and insightful answer to a fundamentally mis-stated question.

Many ++ to Corion for truly humble monkish patience, forbearance and generosity in dealing with a miserable sinner.